Homeostasis

Claude Bernard is acknowledged to be one of the greatest of all biologists and is the father of modern experimental physiology. He was the first scientist given a state funeral in France. Among his many accomplishments were studies on the role of the liver in carbohydrate metabolism, pancreatic secretions in digestion, the influence of the involuntary nervous system on regulating blood pressure, and the nature of the toxicity of carbon monoxide and curare. In his classic work, Introduction to the Study of Experimental Medicine (1865), he described the nature of scientific research and the scientist. His greatest contribution, however, was his 1854 formulation of the milieu intérieur, now referred to as homeostasis (from the Greek “standing still”), which is considered to be one of the unifying principles of modern biology.

Bernard noted that animals reside in two environments: an exterior environment and an interior environment (milieu intérieur). Primitive life forms evolved in the sea, which provided a relatively stable external environment. But with evolution, these life forms moved to unstable terrestrial soundings with respect to the ambient temperature, salt and water composition, and pH. Their survival required adaption mechanisms for keeping their internal environment stable in the face of such changes. Homeostasis is the ability to maintain a constant internal environment in response to an external environmental change. Those life forms and their progeny that successfully achieved homeostasis survived; those that didn’t succumbed.

As these wild geese fight, significant changes occur in their cardiovascular systems and carbohydrate metabolism. Their endocrine and nervous systems play major roles in restoring and maintaining the homeostatic balance in their bodies after the conflict concludes.

Bernard’s concept of milieu intérieur largely languished until the early years of the twentieth century when it was renamed homeostasis and popularized by W . B. Cannon, of “fight-or-flight fame,” in his 1932 book, The Wisdom of the Body. In it, Cannon described the effort of multiple organs working cooperatively to maintain homeostasis. We now know that the nervous and hormonal systems play a major role in maintaining the homeostatic balance or steady states. To maintain homeostasis, including body temperature, blood sugar levels, and pH of the blood and body fluids, the body employs negative feedback systems in which it responds in an opposite direction to a change.